When sewing, a seam is what holds two pieces of fabric together with a stitched row of thread. How a seam is stitched can affect the look of your finished garmnent. They should be smooth and secure without puckers or stretching or loose threads. The seam type that you use should therefore be suited to your chosen fabric and design of the garment.
Seams Basic Overview:
Most bought sewing patterns have a 1.5cm or 5/8" seam allowance. However you should read through the instructions first, as some areas may have a wider or narrower seam allowance, often at the hem or neckline. When starting or ending a seam, always secure your stitching with a lockstitch or backstitch or even by knotting the threads together.
Before stitching your fabric, the seams may be pinned together at a right angle to the cut edge which allows them to be easily removed when sewing. Alternately you may prefer to baste the seams by hand or machine before sewing the permanent seam. Always know your seam allowance and follow the guide on the foot plate of the sewing machine.
A Neat Finish on Seams:
Any curved areas of the cut fabric may be stay-stitched before sewing, where a line of stitching is sewn within the seam allowance to prevent the curve from stretching when sewn. Seams which are on a bias cut garment may be basted first or stitched with temporary stitching, then the garment may be hung up for a few hours to allow the fabric to rest and ease, then the seam may be stitched. By doing this you can prevent puckered seams when the bias garment is worn.
Stitching corners can be tricky so take your time here. Corners may be reinforced with a stitch just inside of the seam allowance, sewing a line of about 2.5 cm or 1 inch on either side. Stitch up to the adjacent seam allowance and with your needle in the fabric, lift your sewing machine foot and swivel the fabric around toward the next seam. If you are stitching a straight piece of fabric to a corner, making an upright piece like a box, then clip into the corner just up to the sewing line. You may then swivel the straight fabric around to line up with the other edge of the corner, then lower your machine foot and continue stitching.
Curved seams must be clipped into to sit smoothly and flat. For convex or outer curved seams, cut out small triangular notches at regular intervals (shown on the left side of the photos alongside). For inward or concave seams, clip into the seam at regular intervals (shown on the right side of the photos alongside). The tighter the curve, the more notches you will need. Any bulky seams may also
be trimmed down to varying widths to reduce fulness; this is called "grading" a seam.
Any enclosed or bagged out edges should be under-stitched to give a crisp finish and to stop the inside fabric from rolling out. This would be done on facings, linings or collars which are not top stitched. Just remember that if the seam is curved, this needs to be clipped or notched before under-stitching. An under-stitch is done with the right side of the fabric face up and the seam allowance pressed toward the facing. A row of stitching is then done about 2mm from the seam, catching the seam allowance to the facing.
Seams should be well ironed, preferably from the wrong side and may be pressed open or closed and also finished by overlocking, over casting or with a zigzag stitch on the edge.
Enclosed Seams:
Some seams may be enclosed within the seam allowance which creates a clean finish especially on sheer fabrics or where you would like a more professional finish inside the garment.
A French seam is a neat enclosed seam, best suited for straight seams. The seam is stitched about 7mm inside from the stitch line with wrong sides of the fabric together. Trim the seam to about 3mm, then turn the fabric to be right sides together enclosing the first seam, stitching now on the actual seam line. The photo alongside shows a completed French seam on the left and the seam construction on the right.
A Mock French seam looks similar to a French seam on the inside of a garment, but there is a visible stitch on the seam allowance. Stitch a normal seam with wrong fabric sides together, then turn both seam allowances in on each other and edge stitch them together.
A Self-Bound seam is similar to a Mock French seam where a standard seam is stitched then one seam allowance is trimmed down to 3mm or 1/8”. The other seam allowance is then turned over the cut edge and slip stitched or machine stitched in place.
A Flat Felled seam is a strong seam often used on sportswear or heavy workwear. A seam is sewn with wrong fabric sides together then the back-most seam is trimmed to about 3mm. The wider seam allowance is then folded over the edge of the narrow seam and stitched flat over the trimmed seam. There are therefore two visible rows of stitching on the outside of the garment.
Decorative Seams:
Seams can be finished is a way which adds to their character and draws attention with topstitching which can be sewn in thicker thread or in contrasting colours. Top stitching may be done on most standard seams but may not be suitable for lightweight or sheer fabrics. On the right side of the fabric, topstitch 1-2mm from the seam fold with both seam allowances caught in the stitching. A double topstitch can be done when the seams are open underneath and a top stitch is sewn 1-2mm from the seam on both sides.
A Welt seam looks similar to a Flat Fell seam from the outside, however the seam is on the inside of the garment and is not enclosed. Stitch a standard seam and then trim one side to about 5mm or 1/4” then encase this seam with the untrimmed side and top stitch about 6mm from the seam on the right side of the fabric. A double Welt seam is the same process, but add another stitch about 1mm from the seam on the right side of the fabric. The left side of the photo shows a Welt seam and the right side shows a double Welt seam.
The seams mentioned here are only a few of those which you may choose from. Some are to add strength, some to add interest and some are for practical reasons. If you are unsure of which seam would suit your project the best, try a few options on scarp fabric; press the seams, pull them to check their strength and check your needles and tension to see if the seam quality is good.
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